Relative positioning of balloons with altitude control and wind data

ABSTRACT

The positions of balloons in a communication network of balloons, such as a mesh network of high-altitude balloons, may be adjusted relative to one another in order to try to maintain a desired network topology. In one approach, the position of each balloon may be adjusted relative to one or more neighbor balloons. For example, the locations of a target balloon and one or more neighbor balloons may be determined. A desired movement of the target balloon may then be determined based on the locations of the one or more neighbor balloons relative to the location of the target balloon. The target balloon may be controlled based on the desired movement. In some embodiments, the altitude of the target balloon may be controlled in order to expose the target balloon to ambient winds that are capable of producing the desired movement of the target balloon.

BACKGROUND

Unless otherwise indicated herein, the materials described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

Computing devices such as personal computers, laptop computers, tabletcomputers, cellular phones, and countless types of Internet-capabledevices are increasingly prevalent in numerous aspects of modern life.As such, the demand for data connectivity via the Internet, cellulardata networks, and other such networks, is growing. However, there aremany areas of the world where data connectivity is still unavailable, orif available, is unreliable and/or costly. Accordingly, additionalnetwork infrastructure is desirable.

SUMMARY

In a first aspect, a method is provided. The method includes determininga location of a target balloon and determining locations of one or moreneighbor balloons relative to the location of the target balloon. Thetarget balloon includes a communication system that is operable for datacommunication with at least one of the one or more neighbor balloons.The method further includes determining a desired movement of the targetballoon based on the locations of the one or more neighbor balloonsrelative to the location of the target balloon and controlling thetarget balloon based on the desired movement of the target balloon.

In a second aspect, a non-transitory computer readable medium isprovided. The non-transitory computer readable medium has stored thereininstructions executable by a computing device to cause the computingdevice to perform functions. The functions include: (a) determining alocation of a target balloon; (b) determining locations of one or moreneighbor balloons relative to the location of the target balloon; (c)determining a desired movement of the target balloon based on thelocations of the one or more neighbor balloons relative to the locationof the target balloon; and (d) controlling the target balloon based onthe desired movement of the target balloon.

In a third aspect, a balloon is provided. The balloon includes acommunication system operable for data communications with one of moreother balloons in a mesh network of balloons. The balloon furtherincludes a controller coupled to the communication system. Thecontroller is configured to: (a) determine the balloon's location; (b)determine locations of one or more neighbor balloons relative to theballoon's location, wherein the one or more neighbor balloons are in themesh network of balloons; and (c) determine a desired movement of theballoon based on the locations of the one or more neighbor balloonsrelative to the balloon's location.

In a fourth aspect, a method is provided. The method includesidentifying a plurality of goodness factors for a given balloon in ahigh-altitude balloon network, and determining a plurality of goodnessscores for the given balloon. Each goodness score relates to arespective goodness factor in the plurality of goodness factors. Themethod also includes determining a current overall goodness for thegiven balloon as a function of the plurality of goodness scores for thegiven balloon. The method further includes identifying a plurality ofactions that could be taken by the given balloon and determining, foreach action, a respective overall goodness resulting from that action.Still further, the method includes selecting, from among the pluralityof actions, an action that results in an overall goodness that is higherthan the current overall goodness and controlling the given balloon toundertake the selected action.

In a fifth aspect, a non-transitory computer readable medium isprovided. The non-transitory computer readable medium has stored thereininstructions executable by a computing device to cause the computingdevice to perform functions. The functions include: (a) identifying aplurality of goodness factors for a given balloon in a high-altitudeballoon network; (b) determining a plurality of goodness scores for thegiven balloon, where each goodness score relates to a respectivegoodness factor in the plurality of goodness factors; (c) determining acurrent overall goodness for the given balloon as a function of theplurality of goodness scores for the given balloon; (d) identifying aplurality of actions that could be taken by the given balloon; (e)determining, for each action, a respective overall goodness resultingfrom that action; (f) selecting, from among the plurality of actions, anaction that results in an overall goodness that is higher than thecurrent overall goodness; and (g) controlling the given balloon toundertake the selected action.

These as well as other aspects, advantages, and alternatives, willbecome apparent to those of ordinary skill in the art by reading thefollowing detailed description, with reference where appropriate to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram illustrating a balloon network,according to an example embodiment.

FIG. 2 is a block diagram illustrating a balloon-network control system,according to an example embodiment.

FIG. 3 is a simplified block diagram illustrating a high-altitudeballoon, according to an example embodiment.

FIG. 4 is a simplified block diagram illustrating a balloon network thatincludes super-nodes and sub-nodes, according to an example embodiment.

FIG. 5 illustrates a scenario for determining a desired movement of atarget balloon based on the locations of four neighbor balloons,according to an example embodiment.

FIG. 6 is a flowchart illustrating a method, according to an exampleembodiment.

DETAILED DESCRIPTION

Example methods and systems are described herein. Any example embodimentor feature described herein is not necessarily to be construed aspreferred or advantageous over other embodiments or features. Theexample embodiments described herein are not meant to be limiting. Itwill be readily understood that certain aspects of the disclosed systemsand methods can be arranged and combined in a wide variety of differentconfigurations, all of which are contemplated herein.

Furthermore, the particular arrangements shown in the Figures should notbe viewed as limiting. It should be understood that other embodimentsmay include more or less of each element shown in a given Figure.Further, some of the illustrated elements may be combined or omitted.Yet further, an example embodiment may include elements that are notillustrated in the Figures.

1. Overview

Example embodiments help to provide a data network that includes aplurality of balloons; for example, a mesh network formed byhigh-altitude balloons deployed in the stratosphere. Since winds in thestratosphere may affect the locations of the balloons in a differentialmanner, each balloon in an example network may be configured to changeits horizontal position by adjusting its vertical position (i.e.,altitude). For instance, by adjusting its altitude, a balloon may beable find winds that will carry it horizontally (e.g., latitudinallyand/or longitudinally) to a desired horizontal location.

Further, in an example balloon network, the balloons may communicatewith one another using free-space optical communications. For instance,the balloons may be configured for optical communications usingultra-bright LEDs (which are also referred to as “high-power” or“high-output” LEDs). In some instances, lasers could be used instead ofor in addition to LEDs, although regulations for laser communicationsmay restrict laser usage. In addition, the balloons may communicate withground-based station(s) using radio-frequency (RF) communications.

In some embodiments, a high-altitude-balloon network may be homogenous.That is, the balloons in a high-altitude-balloon network could besubstantially similar to each other in one or more ways. Morespecifically, in a homogenous high-altitude-balloon network, eachballoon is configured to communicate with one or more other balloons viafree-space optical links. Further, some or all of the balloons in such anetwork, may additionally be configured to communicate with ground-basedand/or satellite-based station(s) using RF and/or opticalcommunications. Thus, in some embodiments, the balloons may behomogenous in so far as each balloon is configured for free-spaceoptical communication with other balloons, but heterogeneous with regardto RF communications with ground-based stations.

In other embodiments, a high-altitude-balloon network may beheterogeneous, and thus may include two or more different types ofballoons. For example, some balloons in a heterogeneous network may beconfigured as super-nodes, while other balloons may be configured assub-nodes. It is also possible that some balloons in a heterogeneousnetwork may be configured to function as both a super-node and asub-node. Such balloons may function as either a super-node or asub-node at a particular time, or, alternatively, act as bothsimultaneously depending on the context. For instance, an exampleballoon could aggregate search requests of a first type to transmit to aground-based station. The example balloon could also send searchrequests of a second type to another balloon, which could act as asuper-node in that context. Further, some balloons, which may besuper-nodes in an example embodiment, can be configured to communicatevia optical links with ground-based stations and/or satellites.

In n example configuration, the super-node balloons may be configured tocommunicate with nearby super-node balloons via free-space opticallinks. However, the sub-node balloons may not be configured forfree-space optical communication, and may instead be configured for someother type of communication, such as RF communications. In that case, asuper-node may be further configured to communicate with sub-nodes usingRF communications. Thus, the sub-nodes may relay communications betweenthe super-nodes and one or more ground-based stations using RFcommunications. In this way, the super-nodes may collectively functionas backhaul for the balloon network, while the sub-nodes function torelay communications from the super-nodes to ground-based stations.Other differences could be present between balloons in a heterogeneousballoon network.

The present disclosure describes various example embodiments ofapparatuses, methods, and functions executable by a computer-readablemedium that are generally operable to determine a desired movement of atarget balloon, based on the locations of one or more neighbor balloonsrelative to the location of the target balloon, and to control thetarget balloon based on the desired movement.

In some embodiments, a potential energy function may be defined thatassigns a potential energy to the target balloon as a function of thelocations of the one or more neighbor balloons and the location of thetarget balloon. A gradient of the potential energy function may bedetermined, and the desired movement of the target balloon may bedetermined based on the gradient.

In some embodiments, the desired movement of the target balloon is ahorizontal movement that may be achieved by controlling the altitude ofthe target balloon. For example, wind data and/or predictive models maybe used to determine that ambient winds with a velocity that is suitableto achieve the desired horizontal movement are likely to be available ata particular altitude. The altitude of the target balloon may then beadjusted to attain the particular altitude.

2. Example Balloon Networks

FIG. 1 is a simplified block diagram illustrating a balloon network 100,according to an example embodiment. As shown, balloon network 100includes balloons 102A to 102F, which are configured to communicate withone another via free-space optical links 104. Balloons 102A to 102Fcould additionally or alternatively be configured to communicate withone another via RF links 114. Balloons 102A to 102F may collectivelyfunction as a mesh network for packet-data communications. Further, atleast some of balloons 102A and 102B may be configured for RFcommunications with ground-based stations 106 and 112 via respective RFlinks 108. Further, some balloons, such as balloon 102F, could beconfigured to communicate via optical link 110 with ground-based station112.

In an example embodiment, balloons 102A to 102F are high-altitudeballoons, which are deployed in the stratosphere. At moderate latitudes,the stratosphere includes altitudes between approximately 10 kilometers(km) and 50 km altitude above the surface. At the poles, thestratosphere starts at an altitude of approximately 8 km. In an exampleembodiment, high-altitude balloons may be generally configured tooperate in an altitude range within the stratosphere that has relativelylow wind speed (e.g., between 5 and 20 miles per hour (mph)).

More specifically, in a high-altitude-balloon network, balloons 102A to102F may generally be configured to operate at altitudes between 18 kmand 25 km (although other altitudes are possible). This altitude rangemay be advantageous for several reasons. In particular, this layer ofthe stratosphere generally has relatively low wind speeds (e.g., windsbetween 5 and 20 mph) and relatively little turbulence. Further, whilethe winds between 18 km and 25 km may vary with latitude and by season,the variations can be modeled in a reasonably accurate manner.Additionally, altitudes above 18 km are typically above the maximumflight level designated for commercial air traffic. Therefore,interference with commercial flights is not a concern when balloons aredeployed between 18 km and 25 km.

To transmit data to another balloon, a given balloon 102A to 102F may beconfigured to transmit an optical signal via an optical link 104. In anexample embodiment, a given balloon 102A to 102F may use one or morehigh-power light-emitting diodes (LEDs) to transmit an optical signal.Alternatively, some or all of balloons 102A to 102F may include lasersystems for free-space optical communications over optical links 104.Other types of free-space optical communication are possible. Further,in order to receive an optical signal from another balloon via anoptical link 104, a given balloon 102A to 102F may include one or moreoptical receivers. Additional details of example balloons are discussedin greater detail below, with reference to FIG. 3.

In a further aspect, balloons 102A to 102F may utilize one or more ofvarious different RF air-interface protocols for communication withground-based stations 106 and 112 via respective RF links 108. Forinstance, some or all of balloons 102A to 102F may be configured tocommunicate with ground-based stations 106 and 112 using protocolsdescribed in IEEE 802.11 (including any of the IEEE 802.11 revisions),various cellular protocols such as GSM, CDMA, UMTS, EV-DO, WiMAX, and/orLTE, and/or one or more propriety protocols developed for balloon-groundRF communication, among other possibilities.

In a further aspect, there may be scenarios where RF links 108 do notprovide a desired link capacity for balloon-to-ground communications.For instance, increased capacity may be desirable to provide backhaullinks from a ground-based gateway, and in other scenarios as well.Accordingly, an example network may also include downlink balloons,which could provide a high-capacity air-ground link.

For example, in balloon network 100, balloon 102F is configured as adownlink balloon. Like other balloons in an example network, a downlinkballoon 102F may be operable for optical communication with otherballoons via optical links 104. However, a downlink balloon 102F mayalso be configured for free-space optical communication with aground-based station 112 via an optical link 110. Optical link 110 maytherefore serve as a high-capacity link (as compared to an RF link 108)between the balloon network 100 and the ground-based station 112.

Note that in some implementations, a downlink balloon 102F mayadditionally be operable for RF communication with ground-based stations106. In other cases, a downlink balloon 102F may only use an opticallink for balloon-to-ground communications. Further, while thearrangement shown in FIG. 1 includes just one downlink balloon 102F, anexample balloon network can also include multiple downlink balloons. Onthe other hand, a balloon network can also be implemented without anydownlink balloons.

In other implementations, a downlink balloon may be equipped with aspecialized, high-bandwidth RF communication system forballoon-to-ground communications, instead of, or in addition to, afree-space optical communication system. The high-bandwidth RFcommunication system may take the form of an ultra-wideband system,which may provide an RF link with substantially the same capacity as oneof the optical links 104. Other forms are also possible.

Ground-based stations, such as ground-based stations 106 and/or 112, maytake various forms. Generally, a ground-based station may includecomponents such as transceivers, transmitters, and/or receivers forcommunication via RF links and/or optical links with a balloon network.Further, a ground-based station may use various air-interface protocolsin order to communicate with a balloon 102A to 102F over an RF link 108.As such, ground-based stations 106 and 112 may be configured as anaccess point via which various devices can connect to balloon network100. Ground-based stations 106 and 112 may have other configurationsand/or serve other purposes without departing from the scope of theinvention.

In a further aspect, some or all of balloons 102A to 102F could beconfigured to establish a communication link with space-based satellitesin addition to, or as an alternative to, a ground-based communicationlink. In some embodiments, a balloon may communicate with a satellitevia an optical link. However, other types of satellite communicationsare possible.

Further, some ground-based stations, such as ground-based stations 106and 112, may be configured as gateways between balloon network 100 andone or more other networks. Such ground-based stations 106 and 112 maythus serve as an interface between the balloon network and the Internet,a cellular service provider's network, and/or other types of networks.Variations on this configuration and other configurations ofground-based stations 106 and 112 are also possible.

2a) Mesh Network Functionality

As noted, balloons 102A to 102F may collectively function as a meshnetwork. More specifically, since balloons 102A to 102F may communicatewith one another using free-space optical links, the balloons maycollectively function as a free-space optical mesh network.

In a mesh-network configuration, each balloon 102A to 102F may functionas a node of the mesh network, which is operable to receive datadirected to it and to route data to other balloons. As such, data may berouted from a source balloon to a destination balloon by determining anappropriate sequence of optical links between the source balloon and thedestination balloon. These optical links may be collectively referred toas a “lightpath” for the connection between the source and destinationballoons. Further, each of the optical links may be referred to as a“hop” on the lightpath.

To operate as a mesh network, balloons 102A to 102F may employ variousrouting techniques and self-healing algorithms. In some embodiments, aballoon network 100 may employ adaptive or dynamic routing, where alightpath between a source and destination balloon is determined andset-up when the connection is needed, and released at a later time.Further, when adaptive routing is used, the lightpath may be determineddynamically depending upon the current state, past state, and/orpredicted state of the balloon network.

In addition, the network topology may change as the balloons 102A to102F move relative to one another and/or relative to the ground.Accordingly, an example balloon network 100 may apply a mesh protocol toupdate the state of the network as the topology of the network changes.For example, to address the mobility of the balloons 102A to 102F,balloon network 100 may employ and/or adapt various techniques that areemployed in mobile ad hoc networks (MANETs). Other examples are possibleas well.

In some implementations, a balloon network 100 may be configured as atransparent mesh network. More specifically, in a transparent balloonnetwork, the balloons may include components for physical switching thatis entirely optical, without any electrical components involved in thephysical routing of optical signals. Thus, in a transparentconfiguration with optical switching, signals travel through a multi-hoplightpath that is entirely optical.

In other implementations, the balloon network 100 may implement afree-space optical mesh network that is opaque. In an opaqueconfiguration, some or all balloons 102A to 102F may implementoptical-electrical-optical (OEO) switching. For example, some or allballoons may include optical cross-connects (OXCs) for OEO conversion ofoptical signals. Other opaque configurations are also possible.Additionally, network configurations are possible that include routingpaths with both transparent and opaque sections.

In a further aspect, balloons in an example balloon network 100 mayimplement wavelength division multiplexing (WDM), which may help toincrease link capacity. When WDM is implemented with transparentswitching, physical lightpaths through the balloon network may besubject to the “wavelength continuity constraint.” More specifically,because the switching in a transparent network is entirely optical, itmay be necessary to assign the same wavelength for all optical links ona given lightpath.

An opaque configuration, on the other hand, may avoid the wavelengthcontinuity constraint. In particular, balloons in an opaque balloonnetwork may include the OEO switching systems operable for wavelengthconversion. As a result, balloons can convert the wavelength of anoptical signal at each hop along a lightpath. Alternatively, opticalwavelength conversion could take place at only selected hops along thelightpath.

Further, various routing algorithms may be employed in an opaqueconfiguration. For example, to determine a primary lightpath and/or oneor more diverse backup lightpaths for a given connection, exampleballoons may apply or consider shortest-path routing techniques such asDijkstra's algorithm and k-shortest path, and/or edge and node-diverseor disjoint routing such as Suurballe's algorithm, among others.Additionally or alternatively, techniques for maintaining a particularquality of service (QoS) may be employed when determining a lightpath.Other techniques are also possible.

2b) Station-Keeping Functionality

In an example embodiment, a balloon network 100 may implementstation-keeping functions to help provide a desired network topology.For example, station-keeping may involve each balloon 102A to 102Fmaintaining and/or moving into a certain position relative to one ormore other balloons in the network (and possibly in a certain positionrelative to the ground). As part of this process, each balloon 102A to102F may implement station-keeping functions to determine its desiredpositioning within the desired topology, and if necessary, to determinehow to move to the desired position.

The desired topology may vary depending upon the particularimplementation. In some cases, balloons may implement station-keeping toprovide a substantially uniform topology. In such cases, a given balloon102A to 102F may implement station-keeping functions to position itselfat substantially the same distance (or within a certain range ofdistances) from adjacent balloons in the balloon network 100.

In other cases, a balloon network 100 may have a non-uniform topology.For instance, example embodiments may involve topologies where balloonsare distributed more or less densely in certain areas, for variousreasons. As an example, to help meet the higher bandwidth demands thatare typical in urban areas, balloons may be clustered more densely overurban areas. For similar reasons, the distribution of balloons may bedenser over land than over large bodies of water. Many other examples ofnon-uniform topologies are possible.

In a further aspect, the topology of an example balloon network may beadaptable. In particular, station-keeping functionality of exampleballoons may allow the balloons to adjust their respective positioningin accordance with a change in the desired topology of the network. Forexample, one or more balloons could move to new positions to increase ordecrease the density of balloons in a given area. Other examples arepossible.

In some embodiments, a balloon network 100 may employ an energy functionto determine if and/or how balloons should move to provide a desiredtopology. In particular, the state of a given balloon and the states ofsome or all nearby balloons may be input to an energy function. Theenergy function may apply the current states of the given balloon andthe nearby balloons to a desired network state (e.g., a statecorresponding to the desired topology). A vector indicating a desiredmovement of the given balloon may then be determined by determining thegradient of the energy function. The given balloon may then determineappropriate actions to take in order to effectuate the desired movement.For example, a balloon may determine an altitude adjustment oradjustments such that winds will move the balloon in the desired manner.

2c) Control of Balloons in a Balloon Network

In some embodiments, mesh networking and/or station-keeping functionsmay be centralized. For example, FIG. 2 is a block diagram illustratinga balloon-network control system, according to an example embodiment. Inparticular, FIG. 2 shows a distributed control system, which includes acentral control system 200 and a number of regional control-systems 202Ato 202B. Such a control system may be configured to coordinate certainfunctionality for balloon network 204, and as such, may be configured tocontrol and/or coordinate certain functions for balloons 206A to 206I.

In the illustrated embodiment, central control system 200 may beconfigured to communicate with balloons 206A to 206I via a number ofregional control systems 202A to 202C. These regional control systems202A to 202C may be configured to receive communications and/oraggregate data from balloons in the respective geographic areas thatthey cover, and to relay the communications and/or data to centralcontrol system 200. Further, regional control systems 202A to 202C maybe configured to route communications from central control system 200 tothe balloons in their respective geographic areas. For instance, asshown in FIG. 2, regional control system 202A may relay communicationsand/or data between balloons 206A to 206C and central control system200, regional control system 202B may relay communications and/or databetween balloons 206D to 206F and central control system 200, andregional control system 202C may relay communications and/or databetween balloons 206G to 206I and central control system 200.

In order to facilitate communications between the central control system200 and balloons 206A to 206I, certain balloons may be configured asdownlink balloons, which are operable to communicate with regionalcontrol systems 202A to 202C. Accordingly, each regional control system202A to 202C may be configured to communicate with the downlink balloonor balloons in the respective geographic area it covers. For example, inthe illustrated embodiment, balloons 206A, 206F, and 206I are configuredas downlink balloons. As such, regional control systems 202A to 202C mayrespectively communicate with balloons 206A, 206F, and 206I via opticallinks 206, 208, and 210, respectively.

In the illustrated configuration, only some of balloons 206A to 206I areconfigured as downlink balloons. The balloons 206A, 206F, and 206I thatare configured as downlink balloons may relay communications fromcentral control system 200 to other balloons in the balloon network,such as balloons 206B to 206E, 206G, and 206H. However, it should beunderstood that in some implementations, it is possible that allballoons may function as downlink balloons. Further, while FIG. 2 showsmultiple balloons configured as downlink balloons, it is also possiblefor a balloon network to include only one downlink balloon, or possiblyeven no downlink balloons.

Note that a regional control system 202A to 202C may in fact just be aparticular type of ground-based station that is configured tocommunicate with downlink balloons (e.g., such as ground-based station112 of FIG. 1). Thus, while not shown in FIG. 2, a control system may beimplemented in conjunction with other types of ground-based stations(e.g., access points, gateways, etc.).

In a centralized control arrangement, such as that shown in FIG. 2, thecentral control system 200 (and possibly regional control systems 202Ato 202C as well) may coordinate certain mesh-networking functions forballoon network 204. For example, balloons 206A to 206I may send thecentral control system 200 certain state information, which the centralcontrol system 200 may utilize to determine the state of balloon network204. The state information from a given balloon may include locationdata, optical-link information (e.g., the identity of other balloonswith which the balloon has established an optical link, the bandwidth ofthe link, wavelength usage and/or availability on a link, etc.), winddata collected by the balloon, and/or other types of information.Accordingly, the central control system 200 may aggregate stateinformation from some or all of the balloons 206A to 206I in order todetermine an overall state of the network.

The overall state of the network may then be used to coordinate and/orfacilitate certain mesh-networking functions such as determininglightpaths for connections. For example, the central control system 200may determine a current topology based on the aggregate stateinformation from some or all of the balloons 206A to 206I. The topologymay provide a picture of the current optical links that are available inballoon network and/or the wavelength availability on the links. Thistopology may then be sent to some or all of the balloons so that arouting technique may be employed to select appropriate lightpaths (andpossibly backup lightpaths) for communications through the balloonnetwork 204.

In a further aspect, the central control system 200 (and possiblyregional control systems 202A to 202C as well) may also coordinatecertain station-keeping functions for balloon network 204. For example,the central control system 200 may input state information that isreceived from balloons 206A to 206I to an energy function, which mayeffectively compare the current topology of the network to a desiredtopology, and provide a vector indicating a direction of movement (ifany) for each balloon, such that the balloons can move towards thedesired topology. Further, the central control system 200 may usealtitudinal wind data to determine respective altitude adjustments thatmay be initiated to achieve the movement towards the desired topology.The central control system 200 may provide and/or support otherstation-keeping functions as well.

FIG. 2 shows a distributed arrangement that provides centralizedcontrol, with regional control systems 202A to 202C coordinatingcommunications between a central control system 200 and a balloonnetwork 204. Such an arrangement may be useful to provide centralizedcontrol for a balloon network that covers a large geographic area. Insome embodiments, a distributed arrangement may even support a globalballoon network that provides coverage everywhere on earth. Of course, adistributed-control arrangement may be useful in other scenarios aswell.

Further, it should be understood that other control-system arrangementsare also possible. For instance, some implementations may involve acentralized control system with additional layers (e.g., sub-regionsystems within the regional control systems, and so on). Alternatively,control functions may be provided by a single, centralized, controlsystem, which communicates directly with one or more downlink balloons.

In some embodiments, control and coordination of a balloon network maybe shared by a ground-based control system and a balloon network tovarying degrees, depending upon the implementation. In fact, in someembodiments, there may be no ground-based control systems. In such anembodiment, all network control and coordination functions may beimplemented by the balloon network itself. For example, certain balloonsmay be configured to provide the same or similar functions as centralcontrol system 200 and/or regional control systems 202A to 202C. Otherexamples are also possible.

Furthermore, control and/or coordination of a balloon network may bede-centralized. For example, each balloon may relay state informationto, and receive state information from, some or all nearby balloons.Further, each balloon may relay state information that it receives froma nearby balloon to some or all nearby balloons. When all balloons doso, each balloon may be able to individually determine the state of thenetwork. Alternatively, certain balloons may be designated to aggregatestate information for a given portion of the network. These balloons maythen coordinate with one another to determine the overall state of thenetwork.

Further, in some aspects, control of a balloon network may be partiallyor entirely localized, such that it is not dependent on the overallstate of the network. For example, individual balloons may implementstation-keeping functions that only consider nearby balloons. Inparticular, each balloon may implement an energy function that takesinto account its own state and the states of nearby balloons. The energyfunction may be used to maintain and/or move to a desired position withrespect to the nearby balloons, without necessarily considering thedesired topology of the network as a whole. However, when each balloonimplements such an energy function for station-keeping, the balloonnetwork as a whole may maintain and/or move towards the desiredtopology.

As an example, each balloon A may receive distance information d₁ tod_(k) with respect to each of its k closest neighbors. Each balloon Amay treat the distance to each of the k balloons as a virtual springwith vector representing a force direction from the first nearestneighbor balloon i toward balloon A and with force magnitudeproportional to d_(i). The balloon A may sum each of the k vectors andthe summed vector is the vector of desired movement for balloon A.Balloon A may attempt to achieve the desired movement by controlling itsaltitude.

Alternatively, this process could assign the force magnitude of each ofthese virtual forces equal to d_(i)×d_(i), wherein d_(i) is proportionalto the distance to the second nearest neighbor balloon, for instance.Other algorithms for assigning force magnitudes for respective balloonsin a mesh network are possible.

In another embodiment, a similar process could be carried out for eachof the k balloons and each balloon could transmit its planned movementvector to its local neighbors. Further rounds of refinement to eachballoon's planned movement vector can be made based on the correspondingplanned movement vectors of its neighbors. It will be evident to thoseskilled in the art that other algorithms could be implemented in aballoon network in an effort to maintain a set of balloon spacingsand/or a specific network capacity level over a given geographiclocation.

2d) Example Balloon Configuration

Various types of balloon systems may be incorporated in an exampleballoon network. As noted above, an example embodiment may utilizehigh-altitude balloons, which could typically operate in an altituderange between 18 km and 25 km. FIG. 3 shows a high-altitude balloon 300,according to an example embodiment. As shown, the balloon 300 includesan envelope 302, a skirt 304, a payload 306, and a cut-down system 308,which is attached between the balloon 302 and payload 304.

The envelope 302 and skirt 304 may take various forms, which may becurrently well-known or yet to be developed. For instance, the envelope302 and/or skirt 304 may be made of materials including metalized Mylaror BoPet. Additionally or alternatively, some or all of the envelope 302and/or skirt 304 may be constructed from a highly-flexible latexmaterial or a rubber material such as chloroprene. Other materials arealso possible. Further, the shape and size of the envelope 302 and skirt304 may vary depending upon the particular implementation. Additionally,the envelope 302 may be filled with various different types of gases,such as helium and/or hydrogen. Other types of gases are possible aswell.

The payload 306 of balloon 300 may include a processor 312 and on-boarddata storage, such as memory 314. The memory 314 may take the form of orinclude a non-transitory computer-readable medium. The non-transitorycomputer-readable medium may have instructions stored thereon, which canbe accessed and executed by the processor 312 in order to carry out theballoon functions described herein. Thus, processor 312, in conjunctionwith instructions stored in memory 314, and/or other components, mayfunction as a controller of balloon 300.

The payload 306 of balloon 300 may also include various other types ofequipment and systems to provide a number of different functions. Forexample, payload 306 may include an optical communication system 316,which may transmit optical signals via an ultra-bright LED system 320,and which may receive optical signals via an optical-communicationreceiver 322 (e.g., a photodiode receiver system). Further, payload 306may include an RF communication system 318, which may transmit and/orreceive RF communications via an antenna system 340.

The payload 306 may also include a power supply 326 to supply power tothe various components of balloon 300. The power supply 326 couldinclude a rechargeable battery. In other embodiments, the power supply326 may additionally or alternatively represent other means known in theart for producing power. In addition, the balloon 300 may include asolar power generation system 327. The solar power generation system 327may include solar panels and could be used to generate power thatcharges and/or is distributed by the power supply 326.

The payload 306 may additionally include a positioning system 324. Thepositioning system 324 could include, for example, a global positioningsystem (GPS), an inertial navigation system, and/or a star-trackingsystem. The positioning system 324 may additionally or alternativelyinclude various motion sensors (e.g., accelerometers, magnetometers,gyroscopes, and/or compasses).

The positioning system 324 may additionally or alternatively include oneor more video and/or still cameras, and/or various sensors for capturingenvironmental data.

Some or all of the components and systems within payload 306 may beimplemented in a radiosonde or other probe, which may be operable tomeasure, e.g., pressure, altitude, geographical position (latitude andlongitude), temperature, relative humidity, and/or wind speed and/orwind direction, among other information.

As noted, balloon 300 includes an ultra-bright LED system 320 forfree-space optical communication with other balloons. As such, opticalcommunication system 316 may be configured to transmit a free-spaceoptical signal by modulating the ultra-bright LED system 320. Theoptical communication system 316 may be implemented with mechanicalsystems and/or with hardware, firmware, and/or software. Generally, themanner in which an optical communication system is implemented may vary,depending upon the particular application. The optical communicationsystem 316 and other associated components are described in furtherdetail below.

In a further aspect, balloon 300 may be configured for altitude control.For instance, balloon 300 may include a variable buoyancy system, whichis configured to change the altitude of the balloon 300 by adjusting thevolume and/or density of the gas in the balloon 300. A variable buoyancysystem may take various forms, and may generally be any system that canchange the volume and/or density of gas in the envelope 302.

In an example embodiment, a variable buoyancy system may include abladder 310 that is located inside of envelope 302. The bladder 310could be an elastic chamber configured to hold liquid and/or gas.Alternatively, the bladder 310 need not be inside the envelope 302. Forinstance, the bladder 310 could be a rigid bladder that could bepressurized well beyond neutral pressure. The buoyancy of the balloon300 may therefore be adjusted by changing the density and/or volume ofthe gas in bladder 310. To change the density in bladder 310, balloon300 may be configured with systems and/or mechanisms for heating and/orcooling the gas in bladder 310. Further, to change the volume, balloon300 may include pumps or other features for adding gas to and/orremoving gas from bladder 310. Additionally or alternatively, to changethe volume of bladder 310, balloon 300 may include release valves orother features that are controllable to allow gas to escape from bladder310. Multiple bladders 310 could be implemented within the scope of thisdisclosure. For instance, multiple bladders could be used to improveballoon stability.

In an example embodiment, the envelope 302 could be filled with helium,hydrogen or other lighter-than-air material. The envelope 302 could thushave an associated upward buoyancy force. In such an embodiment, air inthe bladder 310 could be considered a ballast tank that may have anassociated downward ballast force. In another example embodiment, theamount of air in the bladder 310 could be changed by pumping air (e.g.,with an air compressor) into and out of the bladder 310. By adjustingthe amount of air in the bladder 310, the ballast force may becontrolled. In some embodiments, the ballast force may be used, in part,to counteract the buoyancy force and/or to provide altitude stability.

In other embodiments, the envelope 302 could be substantially rigid andinclude an enclosed volume. Air could be evacuated from envelope 302while the enclosed volume is substantially maintained. In other words,at least a partial vacuum could be created and maintained within theenclosed volume. Thus, the envelope 302 and the enclosed volume couldbecome lighter than air and provide a buoyancy force. In yet otherembodiments, air or another material could be controllably introducedinto the partial vacuum of the enclosed volume in an effort to adjustthe overall buoyancy force and/or to provide altitude control.

In another embodiment, a portion of the envelope 302 could be a firstcolor (e.g., black) and/or a first material from the rest of envelope302, which may have a second color (e.g., white) and/or a secondmaterial. For instance, the first color and/or first material could beconfigured to absorb a relatively larger amount of solar energy than thesecond color and/or second material. Thus, rotating the balloon suchthat the first material is facing the sun may act to heat the envelope302 as well as the gas inside the envelope 302. In this way, thebuoyancy force of the envelope 302 may increase. By rotating the balloonsuch that the second material is facing the sun, the temperature of gasinside the envelope 302 may decrease. Accordingly, the buoyancy forcemay decrease. In this manner, the buoyancy force of the balloon could beadjusted by changing the temperature/volume of gas inside the envelope302 using solar energy. In such embodiments, it is possible that abladder 310 may not be a necessary element of balloon 300. Thus, invarious contemplated embodiments, altitude control of balloon 300 couldbe achieved, at least in part, by adjusting the rotation of the balloonwith respect to the sun.

Further, a balloon 306 may include a navigation system (not shown). Thenavigation system may implement station-keeping functions to maintainposition within and/or move to a position in accordance with a desiredtopology. In particular, the navigation system may use altitudinal winddata to determine altitudinal adjustments that result in the windcarrying the balloon in a desired direction and/or to a desiredlocation. The altitude-control system may then make adjustments to thedensity of the balloon chamber in order to effectuate the determinedaltitudinal adjustments and cause the balloon to move laterally to thedesired direction and/or to the desired location. Alternatively, thealtitudinal adjustments may be computed by a ground-based orsatellite-based control system and communicated to the high-altitudeballoon. In other embodiments, specific balloons in a heterogeneousballoon network may be configured to compute altitudinal adjustments forother balloons and transmit the adjustment commands to those otherballoons.

As shown, the balloon 300 also includes a cut-down system 308. Thecut-down system 308 may be activated to separate the payload 306 fromthe rest of balloon 300. The cut-down system 308 could include at leasta connector, such as a balloon cord, connecting the payload 306 to theenvelope 302 and a means for severing the connector (e.g., a shearingmechanism or an explosive bolt). In an example embodiment, the ballooncord, which may be nylon, is wrapped with a nichrome wire. A currentcould be passed through the nichrome wire to heat it and melt the cord,cutting the payload 306 away from the envelope 302.

The cut-down functionality may be utilized anytime the payload needs tobe accessed on the ground, such as when it is time to remove balloon 300from a balloon network, when maintenance is due on systems withinpayload 306, and/or when power supply 326 needs to be recharged orreplaced.

In an alternative arrangement, a balloon may not include a cut-downsystem. In such an arrangement, the navigation system may be operable tonavigate the balloon to a landing location, in the event the balloonneeds to be removed from the network and/or accessed on the ground.Further, it is possible that a balloon may be self-sustaining, such thatit does not need to be accessed on the ground. In yet other embodiments,in-flight balloons may be serviced by specific service balloons oranother type of service aerostat or service aircraft.

2e) Example Heterogeneous Network

In some embodiments, a high-altitude-balloon network may includesuper-node balloons, which communicate with one another via opticallinks, as well as sub-node balloons, which communicate with super-nodeballoons via RF links. Generally, the optical links between super-nodeballoons may be configured to have more bandwidth than the RF linksbetween super-node and sub-node balloons. As such, the super-nodeballoons may function as the backbone of the balloon network, while thesub-nodes may provide sub-networks providing access to the balloonnetwork and/or connecting the balloon network to other networks.

FIG. 4 is a simplified block diagram illustrating a balloon network thatincludes super-nodes and sub-nodes, according to an example embodiment.More specifically, FIG. 4 illustrates a portion of a balloon network 400that includes super-node balloons 410A to 410C (which may also bereferred to as “super-nodes”) and sub-node balloons 420 (which may alsobe referred to as “sub-nodes”).

Each super-node balloon 410A to 410C may include a free-space opticalcommunication system that is operable for packet-data communication withother super-node balloons. As such, super-nodes may communicate with oneanother over optical links. For example, in the illustrated embodiment,super-node 410A and super-node 401B may communicate with one anotherover optical link 402, and super-node 410A and super-node 401C maycommunicate with one another over optical link 404.

Each of the sub-node balloons 420 may include a radio-frequency (RF)communication system that is operable for packet-data communication overone or more RF air interfaces. Accordingly, each super-node balloon 410Ato 410C may include an RF communication system that is operable to routepacket data to one or more nearby sub-node balloons 420. When a sub-node420 receives packet data from a super-node 410, the sub-node 420 may useits RF communication system to route the packet data to a ground-basedstation 430 via an RF air interface.

As noted above, the super-nodes 410A to 410C may be configured for bothlonger-range optical communication with other super-nodes andshorter-range RF communications with nearby sub-nodes 420. For example,super-nodes 410A to 410C may use using high-power or ultra-bright LEDsto transmit optical signals over optical links 402, 404, which mayextend for as much as 100 miles, or possibly more. Configured as such,the super-nodes 410A to 410C may be capable of optical communications atdata rates of 10 to 50 GBit/sec or more.

A larger number of high-altitude balloons may then be configured assub-nodes, which may communicate with ground-based Internet nodes atdata rates on the order of approximately 10 MBit/sec. For instance, inthe illustrated implementation, the sub-nodes 420 may be configured toconnect the super-nodes 410 to other networks and/or directly to clientdevices.

Note that the data speeds and link distances described in the aboveexample and elsewhere herein are provided for illustrative purposes andshould not be considered limiting; other data speeds and link distancesare possible.

In some embodiments, the super-nodes 410A to 410C may function as a corenetwork, while the sub-nodes 420 function as one or more access networksto the core network. In such an embodiment, some or all of the sub-nodes420 may also function as gateways to the balloon network 400.Additionally or alternatively, some or all of ground-based stations 430may function as gateways to the balloon network 400.

3. Example Approaches for Maintaining a Desired Network Topology

The positions of balloons in a high-altitude balloon network may beadjusted in order to maintain a desired network topology. Maintaining adesired network topology may involve maintaining a desired density ofballoons over particular areas, desired altitudes of balloons, a desiredarrangement of particular types of balloons (e.g., super-node balloonsand sub-node balloons), a desired number of “hops” between differentpoints in the network, and/or any other preferences relating to theplacement or arrangement of balloons. For example, it may be desirableto maintain a relatively high density of balloons over densely populatedareas (such as cities or metropolitan areas), whereas a relatively lowdensity of balloons may be sufficient over less populated or unpopulatedareas (such as deserts or oceans). However, even in relativelyunpopulated areas, a certain number and arrangement of balloons may bemaintained in order to provide communication connectivity betweendifferent portions of the network.

In one approach for maintaining a desired network topology, thepositions of balloons may be adjusted relative to locations on theground. For example, the position of a balloon used for downlinkcommunications could be controlled in order to stay within acommunication range of a ground station. Other types of balloons couldalso be controlled to be within a given a range of a specific groundlocation. Thus, a desired arrangement of balloons over a metropolitanarea could be maintained by controlling the positions of the balloons tobe within respective ranges of respective ground positions.

In some cases, there may be an overall flow of balloons throughparticular areas, for example, because of prevailing winds in thestratosphere. In such cases, a desired network topology can still bemaintained based on ground locations. For example, the motion ofballoons relative to one another can be controlled so that when aballoon moves out of range of its respective ground location, areplacement balloon also moves into range. Other examples of maintaininga desired network topology based on ground locations are possible.

In another approach for maintaining a desired network topology, thepositions of balloons may be adjusted relative to each other. Forexample, the position of a target balloon may be adjusted relative toone or more neighbor balloons. The determination of which balloons areincluded as “neighbor balloons” of a target balloon could be made indifferent ways.

In one example, the neighbor balloons could be taken as the N balloonsin the network that are nearest to the target balloon, where N is apredetermined number. N could be as small as one or as large as ten ormore. In some cases, N may be selected for a target balloon based on thewhere the target balloon is located (e.g., N may be larger if the targetballoon is over a highly populated area or smaller if the target balloonis over a less populated area).

In another example, any balloons in the network that are within apredefined distance of the target balloon may be identified as neighborballoons. The predefined distance could depend on where the targetballoon is located (e.g., the predefined distance could be smaller ifthe target balloon is over a highly populated area or larger if thetarget balloon is over a less populated area). Alternatively, thepredefined distance could be taken as the distance over which the targetballoon can communicate with other balloons. Thus, any balloons in thenetwork that are within a communication range of the given balloon maybe identified as neighbor balloons.

The position of the target balloon may be adjusted based on one or moreneighbor balloons in order to maintain a desired distance or a desiredrange of distances between the target balloon and its neighbor balloons.In this regard, one can imagine a virtual spring between the targetballoon and each of its neighbor balloons.

If the distance between the target balloon and a given neighbor balloonis less than the desired distance, then the virtual spring between thetarget n balloon and the given neighbor balloon may be seen ascompressed. The compressed spring may be thought of as exerting avirtual force on the target balloon in a direction away from the givenneighbor balloon. This virtual force may result in the target balloonbeing controlled so as to move away from the given neighbor balloon.

On the other hand, if the distance between the target balloon and thegiven neighbor balloon is greater than the desired distance, then thevirtual spring between the target balloon and the given neighbor balloonmay be seen as stretched. The stretched spring may be thought of asexerting a virtual force on the target balloon in a direction toward thegiven neighbor balloon. This virtual force may result in the targetballoon being controlled so as to move toward the given neighborballoon.

The virtual spring concept may be formalized by using the well-knownpotential energy function for a spring to assign a “potential energy” tothe target balloon as a function of the distance between the targetballoon and the neighbor balloon. The following is one example of such apotential energy function: U=½k(r−R)², where U is the potential energyassigned to the target balloon, k is the “spring constant” of thevirtual spring, r is the actual distance between the target balloon andthe given neighbor balloon, and R is the desired distance between targetballoon and the given neighbor balloon.

Given this potential energy function, the virtual force exerted on thetarget balloon may be expressed as: F=−k(r−R), where F is the virtualforce, k is the spring constant of the virtual spring, r is the actualdistance between the target balloon and the given neighbor balloon, andR is the desired distance between target balloon and the given neighborballoon.

Although the above discussion refers to a potential energy and virtualforce for a target balloon based on only one neighbor balloon, theapproach may be generalized to the case of multiple neighbor balloons.In particular, each of the multiple neighbor balloons may be associatedwith an individual potential energy function, which could be a functionof the respective distance between the target balloon and the neighborballoon in the form described above. Thus, the i^(th) neighbor balloonmay be associated with an individual potential energy function asfollows: U_(i)=½k_(i)(r_(i)−R_(i))², where U_(i) is the i^(th) neighborballoon's contribution to the potential energy of the target balloon,k_(i) is the spring constant for the virtual spring between the targetballoon and the i^(th) neighbor balloon, r_(i) is the actual distancebetween the target balloon and the i^(th) neighbor balloon, and R_(i) isthe desired distance between the target balloon and the i^(th) neighborballoon. As this expression indicates, different neighbor balloons maybe associated with different desired distances and/or different springconstants. The different parameters could reflect, for example,differences in the types or functions of the balloons. For instance, thedesired distances to neighbor balloons that are super-nodes may bedifferent than the desired distances to neighbor balloons that aresub-nodes. Other differences are also possible.

The overall potential energy function for the target balloon may betaken as the sum of the individual potential energy functions from eachof its neighbor balloons: U=ΣU_(i). The virtual force exerted on thetarget balloon may be related to the gradient of the overall potentialenergy function as follows: {right arrow over (F)}=−∇U. Of course, thisvirtual force can also considered to be the vector sum of individualvirtual forces exerted on the target balloon by each of its neighborballoons: {right arrow over (F)}=Σ{right arrow over (F_(t))}.

Because the virtual force exerted on a target balloon includescontributions from each of its neighbor balloons, it is possible for thetarget balloon to move in the general direction of a neighbor balloonthat is already closer than the desired distance (e.g., because anotherneighbor balloon may be even closer). It is also possible for the targetballoon to move generally away from a neighbor balloon that is alreadyfarther than the desired distance (e.g., in order to come closer toanother neighbor balloon that is even more distant). These points areillustrated by scenario 500 shown in FIG. 5.

In scenario 500, a target balloon 502 is shown at the origin of x-ycoordinate axes, and the locations of four neighbor balloons (neighborballoons 504, 506, 508, and 510) are indicated by vectors {right arrowover (r₁)}, {right arrow over (r₂)}, {right arrow over (r₃)}, and {rightarrow over (r₄)}. As shown, neighbor balloon 504 is in the firstquadrant, neighbor balloon 506 is in the second quadrant, neighborballoon 508 is in the third quadrant, and neighbor balloon 510 is in thefourth quadrant. It is to be understood that this arrangement is merelyone example that is presented for purposes of illustration. Targetballoon 502 could have a greater or fewer number of neighbor balloons,and the neighbor balloons could be located differently than shown inFIG. 5.

The x-y coordinates in FIG. 5 may represent ground coordinates. Thus, inaddition to coordinates in the x-y plane, each of balloons 502-510 mayhave respective z-coordinates (i.e., altitudes) which are not indicatedin FIG. 5. Further, the discussion of distances between balloons inscenario 500 may refer to lateral distances in the x-y plane, which donot take into account altitude differences between balloons.

Scenario 500 assumes that the target balloon 502 has the same desireddistance, R, to each of the neighbor balloons 504-510. This desireddistance is indicated by the dashed circle in FIG. 5. As shown, neighborballoons 504 and 508 are more than the desired distance away from targetballoon 502, whereas neighbor balloons 506 and 510 are less than thedesired distance away from target balloon 502.

Each of neighbor balloons 504-510 may exert a respective virtual forceon target balloon 502 based on the “virtual spring” model describedabove. The net virtual force acting on target balloon 502 will be thevector sum of the virtual forces exerted by neighbor balloons 504-510.In particular, neighbor balloons 504 and 508 will both exert anattractive force on target balloon 502 since they are both more than thedesired distance away from target balloon 502. However, neighbor balloon504 is more distant than neighbor balloon 508. Thus, neighbor balloon504 may exert a greater attractive force than neighbor balloon 508. Thenet effect of these attractive forces may be a virtual force toward thefirst quadrant where neighbor balloon 504 is located. Similarly,neighbor balloons 506 and 510 will both exert a repulsive force ontarget balloon 502 since they are both less than the desired distanceaway from target balloon 502. However, neighbor balloon 510 is closerthan neighbor balloon 506. Thus, neighbor balloon 510 may exert agreater repulsive force than neighbor balloon 506. The net effect ofthese repulsive forces may be a virtual force toward the second quadrantwhere neighbor balloon 506 is located. Thus, in scenario 500, theoverall virtual force on target balloon 502, which results from the netattractive forces and the net repulsive forces, may be in a directionthat is generally along the positive y-axis.

The virtual force acting on target balloon 502 may be used to determinea desired movement of target balloon 502. The desired movement could be,for example, a desired velocity, a desired change in velocity, a desiredacceleration, or a desired displacement. Further, the desired movementcould be a horizontal movement (i.e., a movement in the x-y plane), orthe desired movement could include a desired change in altitude. Thetarget balloon 502 could be controlled (e.g., using a controller intarget balloon 502 or through remote control) in order to try to achievethe desired movement, as described in more detail below.

The direction of the desired movement could be based on the direction ofthe virtual force, and the magnitude of the desired movement could bebased on the magnitude of the virtual force. Thus, if the desiredmovement is a desired velocity, then the direction of the desiredvelocity may correspond to the direction of the virtual force, and themagnitude of the desired velocity may be a function of the magnitude ofthe virtual force. In this way, a greater virtual force may result in agreater velocity. If the desired movement is a desired displacement(i.e., a desired distance of travel in a desired direction), then thedesired distance of travel may be a function of the magnitude of thevirtual force and the desired direction of travel may correspond to thedirection of the virtual force. In this way, a greater virtual force mayresult in a greater distance of travel. Thus, whether the desiredmovement is defined in terms of displacement, velocity, acceleration, orsome other parameter, the magnitude of the desired movement of targetballoon 502 may be larger or smaller depending on the magnitude of thevirtual force acting on target balloon 502.

Although the above discussion refers to potential energy functions thatare based on virtual springs, it is to be understood that other types ofpotential energy functions could be used. In general, the potentialenergy, U, of a target balloon may be a function of the locations of thetarget balloon and n neighbor balloons: U({right arrow over (r₀)},{rightarrow over (r₁)}, {right arrow over (r₂)}, . . . {right arrow over(r_(n))}), where n is an integer greater than or equal to one, vector{right arrow over (r₀)} corresponds to the location of the targetballoon, and vectors {right arrow over (r₁)}, {right arrow over (r₂)},through {right arrow over (r_(n))} correspond to the locations of the nneighbor balloons. The locations of the target balloon and the neighborballoon may be in terms of either ground coordinates (i.e., coordinatesin the x-y plane) or to coordinates that include altitude (i.e.,coordinates) in xyz space.

In some embodiments, the potential energy could be a function of thedistances between the target balloon and each of the n neighborballoons. For example, the potential energy, U, could have the followingfunctional form: U=Σu_(i)(|{right arrow over (r₀)}−{right arrow over(r_(l))}|), where u_(i) is a function that is specific to the i^(th)neighbor balloon, and the sum is taken over i=1 to n. The u_(i)functions could be different for different neighbor balloons, or theycould be the same or similar for different neighbor balloons. Forinstance, the u_(i) functions could each correspond to potential energyfunctions based on virtual springs, as discussed above.

The virtual force may be related to the gradient of the potential energyfunction, as follows: {right arrow over (F)}=−∇U({right arrow over(r₀)}, {right arrow over (r₁)}, {right arrow over (r₂)}, . . . {rightarrow over (r_(n))}), where the gradient is determined by taking partialderivatives with respect to the coordinates of the target balloon. Asdiscussed above, the desired movement of the target balloon could bebased on the virtual force and, thus, based on the gradient of thepotential energy function.

The desired movement of the target balloon could also be determined fromthe potential energy function in other ways. For example, the potentialenergy function may have a minimum at coordinates that correspond to adesired location of the target balloon. In that case, the desiredmovement could be a movement toward the desired location, i.e., amovement that minimizes the potential energy function. Other methodscould also be used to determine a desired motion of the target balloonbased on the potential energy function.

Two approaches for maintaining a desired network topology are discussedabove: an approach based on adjusting the positions of balloons relativeto ground locations and an approach based on adjusting the positions ofballoons relative to each other. In addition, these two approaches couldbe combined. For example, the position of a target balloon could beadjusted using an algorithm that takes into account its locationrelative to one or more ground locations as well as its locationrelative to one or more neighbor balloons. The algorithm may involve apotential energy function that includes contributions associated withthe distances between the target balloon and n neighbor balloons andcontributions associated with the distances between the target balloonand p ground locations. The potential energy function could be asfollows: U=Σu_(i)(|{right arrow over (r₀)}−{right arrow over(r_(l))}|)+Σv_(j)(|{right arrow over (r₀)}−{right arrow over (g_(j))}|),where vector {right arrow over (r₀)} corresponds to the location of thetarget balloon, vectors {right arrow over (r_(l))} correspond to thelocations of the n neighbor balloons, u_(i) is a function that isspecific to the i^(th) neighbor balloon, vectors {right arrow over(g_(j))} correspond to the locations of the p ground locations, v_(j) isa function that is specific to the j^(th) ground location, i=1 to n, andj=1 to p. The desired movement of the target balloon may then bedetermined by taking the gradient of the potential energy function, byminimizing the potential energy function, or in some manner.

The concept of a potential energy function may be further generalized asa “goodness” function that can take into account multiple differentkinds of “goodness” factors. Such “goodness” factors may relate to thespacing between balloons, ground locations, altitudes, the wind speedsthat exist near balloons, and/or other types of considerations. Forexample, k “goodness” factors may be identified for a given balloon. Foreach “goodness” factor, a current “goodness” score, G_(i), where i=1 tok, may be determined for the given balloon.

One possible “goodness” factor could be an altitude factor that providesa better “goodness” score for a lower altitude. This type of “goodness”factor may reflect a principle that, all things being equal, it isbetter for a balloon to be lower than higher in order to get a better RFconnection with the ground. Another possible “goodness” factor could bea geographic location factor that provides a better “goodness” score forbeing over certain, desired geographic areas and/or a lower “goodness”score for being over certain geographic areas that should be avoided.This type of “goodness” factor may reflect a principle that, all thingsbeing equal, it is better to be over certain geographic areas thanothers. For example, being over the open ocean may, in general, beassociated with a negative “goodness” score. However, being overshipping lanes in the ocean may be associated with a positive “goodness”score. Other types of factors are also possible.

In addition to determining k “goodness” scores for k “goodness” factorsof a given balloon, it may be possible to consider various actions thatthe given balloon might take in order to improve one or more of these“goodness” scores. Such actions may include, for example, a movement ina particular direction. The movement could be a horizontal movement(i.e., a change in ground position), a vertical movement (i.e., a changein altitude), or a combination of horizontal and vertical movements. Theaction could also be an adjustment in the balloon's buoyancy, anadjustment of an airfoil (a kit, wing, or sail), or some other type ofadjustment that may affect how the balloon moves in response to ambientwinds or under its own power.

A given action, A, may improve one or more “goodness” scores of a givenballoon. However, the action might also adversely affect one or moreother “goodness” scores of the given balloon. Thus, each “goodness”score, G_(i), may be considered a function of the action A, so that wehave G_(i)(A) for the given balloon, where i=1 to k. The overall effectof the action, A, may be determined by calculating an “overallgoodness,” O, as a function of the individual “goodness” scores:O=W(G₁(A), . . . , G_(k)(A)). The function, W, could be any weightingfunction that determines how each “goodness” score contributes to the“overall goodness.” For example, the “goodness” scores could have equalweight, so that the “overall goodness” could simply be the sum of theindividual “goodness” scores. Alternatively, some “goodness” scorescould be weighted more heavily than others, or the relative weightingscould be dependent on the scores themselves.

The merits of a particular action, A, for a given balloon can bedetermined by calculating the resulting “overall goodness,” O, for thatgiven balloon. Various different actions may be evaluated in this way,and the action that maximizes O may be taken as the desired action. Thegiven balloon may then be controlled to undertake the desired action.

By controlling individual balloons based on “goodness” factors, adesired network topology may be achieved. The desired network topologycould be, in a simple case, a network in which the balloons maintain anequal spacing. However, when “goodness” factors other than relativespacing are considered, the desired network topology could be morecomplicated. For example, the relative spacing between balloons could behigher in some areas than in others.

It is also possible to use different techniques for achieving a desirednetwork topology at different times. For example, a default adjustmenttechnique might be applied under typical conditions. However, certainundesirable conditions (such as excessive balloon density) may developfor which a different kind of adjustment technique may be appliedtemporarily (e.g., until the undesirable condition is alleviated).

As one example, when the density of balloons in a particular areabecomes undesirably high, the balloons in that area might “draw lots” insome way (any type of low-probability random selection) to select one ormore balloons to leave the group. A selected balloon could increase ordecrease its altitude until it achieves a speed and direction that ismeaningfully different from that of the group. The selected balloon maythen maintain this different speed and direction for a sufficient periodof time in order to “randomize” the distribution of balloons. At thatpoint, the default adjustment technique may be re-applied. Thisrandomization technique can be used to break up clumps of balloons, witha low probability of clumps re-forming.

4. Example Methods for Achieving a Desired Movement

As noted above, a desired network topology may be maintained byadjusting the positions of individual balloons in the balloon network.The adjustment in the position of a particular, target balloon mayinvolve determining a desired movement of the target balloon (e.g.,based on a potential energy function) and controlling the target balloonto achieve the desired movement. The desired movement of the targetballoon could be achieved in different ways.

In one approach, a desired horizontal movement of the target balloon maybe achieved by adjusting the altitude of the target balloon. In thisregard, the winds in the stratosphere typically follow a pattern inwhich the wind speed decreases with increasing altitude for altitudesbetween about 15 km and 20 km, reaching a local minimum between about 20km and 25 km, and then increases with increasing altitude thereafter. Tothe extent that the target balloon is moving as a result of ambientwinds, the motion of the target balloon can be adjusted by eitherincreasing or decreasing its altitude. For example, altitude control maybe used to achieve a desired horizontal movement of the target balloonby determining that the desired horizontal movement of the targetballoon can be achieved by exposing the target balloon to ambient windsof a particular velocity, determining that ambient winds of theparticular velocity are likely to be available at a particular altitude(this determination could be made based on predictive models and/oractual measurements of the winds in the vicinity of the target balloon),and adjusting the altitude of the target balloon to attain theparticular altitude.

The altitude-adjustment approach can be used in any balloon that isconfigured for altitude control. For example, as discussed above, aballoon may include a variable buoyancy system that can change thevolume and/or density of the gas within the balloon's envelope. However,the altitude-adjustment approach generally relies on the ambient windsto carry the target balloon in the desired direction. Other approachesmay be used to move the target balloon in a direction that is differentthan that of the ambient winds.

For example, the target balloon may include an airfoil, such as a kite,wing, or sail, that can be adjusted to control the target balloon'sdirection of motion. In particular, the airfoil may be operable to movethe target balloon horizontally using ambient winds, but in a directionthat may be controllable (to at least some extent) by appropriateadjustment of the airfoil.

Alternatively, the airfoil may be of a type that is operable to convertvertical motion of the target balloon (the vertical motion may begenerated by changing the buoyancy of the target balloon) intohorizontal motion of the target balloon. This type of airfoil can beused to achieve the desired movement of the target balloon withoutrelying on ambient winds. This approach may be thought of as using theairfoil to convert lift into thrust, which is essentially the oppositeof how a conventional airplane works (the wings of a conventionalairplane convert thrust into lift).

In some embodiments, the target balloon may be configured for poweredflight. For example, the target balloon may include a propeller, jet, orother propulsion mechanism. These propulsion mechanisms may be used toachieve the desired movement of the target balloon instead of or inaddition to the use of ambient winds. Because of the energy that theyconsume, such propulsion mechanisms could be used as a back-up, forexample, when the available ambient winds are insufficient to providethe desired movement.

5. Example Methods for Controlling a Target Balloon Based on theRelative Locations of Neighbor Balloons

FIG. 6 is a flowchart illustrating an example method 600 for controllinga target balloon based on the relative locations of neighbor balloons.Method 600 could be performed using any of the apparatus shown in FIGS.1-5 and described above. However, other configurations could be used.Further, the steps shown in FIG. 6 for method 600 are for one particularembodiment. In other embodiments, the steps may appear in differentorder and steps could be added or subtracted.

Step 602 involves determining a location of a target balloon. The targetballoon could be any balloon whose movement may be controlled, forexample, in order to achieve a desired network topology in a balloonnetwork. For purposes of illustration, this example assumes that thetarget balloon network is in a high-altitude network of balloons thatfunctions as a mesh network. However, other types of balloon networksare possible.

The target balloon could be configured as shown in FIG. 3, or it couldbe differently configured. The location of the target balloon could bedetermined using GPS, inertial navigation data, star-tracking, radar, orby some other method. The location of the target balloon could bedetermined by a positioning system within the target balloon, such aspositioning system 324 shown in FIG. 3. Alternatively, the location ofthe target balloon could be determined externally, for example, byanother balloon, by a ground-based station, or by some other entity.

Step 604 involves determining locations of one or more neighbor balloonsrelative to the determined location of the target balloon. The targetballoon includes a communication system that is operable for datacommunication with at least one of the one or more neighbor balloons.The communication system may, for example, use a free-space optical linkor an RF link for the data communication.

The one or more neighbor balloons may be identified in various ways. Insome embodiments, a predetermined number of balloons in the mesh networkthat are nearest neighbors to the target balloon may be identified asthe one or more neighbor balloons. In other embodiments, any balloons inthe mesh network that are within a predefined distance from the targetballoon may be identified as the one or more neighbor balloons. Thepredefined distance could, for example, correspond to a communicationrange of the target balloon's communication system. Other ways ofdefining which balloons in the mesh network are neighbor balloons to thetarget balloon are also possible.

The locations of the one or more neighbor balloons could be determinedusing GPS, inertial navigation data, star-tracking, radar, or by someother method. The locations of the neighbor balloons could be determinedby the neighbor balloons themselves, and this location information couldbe transmitted to the target balloon, to a ground-based station, or tosome other entity. Alternatively, the locations of the one or moreneighbor balloons could be determined by the target balloon or by aground-based station. Other methods for determining the locations of theone or more neighbor balloons are also possible.

Step 606 involves determining a desired movement of the target balloonbased on the determined locations of the one or more neighbor balloonsrelative to the determined location of the target balloon. The desiredmovement of the target balloon could be a desired displacement of thetarget balloon (such as displacement to a particular location ordisplacement in a certain direction for a certain distance or durationof travel), a desired velocity of the target balloon (the desiredvelocity could be relative to the ground, relative to the air, orrelative to another balloon), a desired change in the velocity of thetarget balloon (either an increase or decrease in the target balloon'scurrent speed and/or a change in the target balloon's current directionof motion), a desired acceleration of the target balloon, or any othertype of movement of the target balloon.

This desired movement could be determined based on a potential energyfunction, as described above. Thus, a potential energy function may bedefined to assign a potential energy to the target balloon as a functionof the determined locations of the one or more neighbor balloons and thedetermined location of the target balloon. A gradient of the potentialenergy function may be determined, and the desired movement of thetarget balloon may be determined based on the gradient of the potentialenergy function. In particular, the direction of the desired movementmay be based on the direction of the gradient and the magnitude of thedesired movement may be based on the magnitude of the gradient.

Step 608 involves controlling the target balloon based on the desiredmovement of the target balloon. In some embodiments, the target balloonmay control itself autonomously to achieve the desired movement, usingdata that the target balloon collects itself or receives through itscommunication system. In other embodiments, the target balloon may becontrolled remotely by another balloon, by a ground-based station, or bysome other entity.

In some embodiments, the desired movement of the target balloon mayinclude a desired horizontal movement (i.e., a movement that isgenerally parallel to the ground). The desired horizontal movement ofthe target balloon may be achieved in various ways.

In one approach, the altitude of the target balloon of the targetballoon may be controlled in order to achieve the desired horizontalmovement of the target balloon. This approach makes use of the variationof wind speed with altitude that is typical in the stratosphere. Forexample, the buoyancy of the target balloon may be adjusted to attain aparticular altitude where ambient ways may be expected to produce thedesired horizontal movement of the target balloon. In some embodiments,the target balloon may use its own predictive models and/or actual dataregarding wind speeds. Alternatively, the target balloon may receivewind data or wind predictions from other balloons, ground-basedstations, and/or other entities.

In another approach, the target balloon may include an airfoil, such asa kite, wing, or sail, that can use ambient winds to achieve the desiredhorizontal movement of the target balloon. For example, the airfoilcould be controllable to achieve a desired direction of movement.

In still another approach, the target balloon may include an airfoilthat is operable to convert vertical motion of the target balloon intothe desired horizontal movement of the target balloon. The verticalmotion of the target balloon may be generated by changing the buoyancyof the target balloon.

In yet another approach, the target balloon may include a propulsionmechanism, such as a propeller or jet. The target balloon may controlthe propulsion mechanism in order to achieve the desired horizontalmovement.

It is to be understood that method 600 shown in FIG. 6 may be performedrepetitively, in order to adjust the position of the target balloonbased on changing conditions. In some embodiments, method 600 may beperformed periodically, for example, every second, minute, or hour. Inother embodiments, method 600 may be performed in response to atriggering event. For example, the target balloon may perform the methodin response to receiving an instruction from another balloon,ground-based station, or some other entity.

It is also to be understood that method 600 shown in FIG. 6 may beperformed in order to adjust the positions of multiple balloons in aballoon network. The method could be performed for each balloonindependently. Alternatively, a central controller, which could be in aballoon or in a ground-based station, may perform the method formultiple balloons in a cooperative fashion. Either way, the positions ofballoons in a balloon network may be adjusted relative to one another inorder to maintain a desired network topology.

6. Non-transitory Computer Readable Media

Some or all of the functions described above and illustrated in FIGS.1-6 may be performed by a computing device in response to the executionof instructions stored in a non-transitory computer readable medium. Thenon-transitory computer readable medium could be, for example, a randomaccess memory (RAM), a read-only memory (ROM), a flash memory, a cachememory, one or more magnetically encoded discs, one or more opticallyencoded discs, or any other form of non-transitory data storage. Thenon-transitory computer readable medium could also be distributed amongmultiple data storage elements, which could be remotely located fromeach other. The computing device that executes the stored instructionscould be a computing device in a balloon, such as a computing devicecorresponding to processor 312 illustrated in FIG. 3. Alternatively, thecomputing device that executes the stored instructions could be inanother entity, such as a ground-based station.

Conclusion

The above detailed description describes various features and functionsof the disclosed systems, devices, and methods with reference to theaccompanying figures. While various aspects and embodiments have beendisclosed herein, other aspects and embodiments will be apparent tothose skilled in the art. The various aspects and embodiments disclosedherein are for purposes of illustration and are not intended to belimiting, with the true scope and spirit being indicated by thefollowing claims.

We claim:
 1. A method comprising: determining a location of a targetballoon; determining locations of one or more neighbor balloons relativeto the determined location of the target balloon, wherein the targetballoon comprises a communication system that is operable for datacommunication with at least one of the one or more neighbor balloons;determining a desired movement of the target balloon based on thedetermined locations of the one or more neighbor balloons relative tothe determined location of the target balloon, wherein the desiredmovement of the target balloon comprises a desired horizontal movementof the target balloon; and controlling the target balloon based on thedesired movement of the target balloon, wherein controlling the targetballoon based on the desired movement of the target balloon comprisescontrolling an altitude of the target balloon based on the desiredhorizontal movement of the target balloon.
 2. The method of claim 1,wherein controlling the altitude of the target balloon based on thedesired horizontal movement of the target balloon comprises: determiningthat the desired horizontal movement of the target balloon can beachieved by exposing the target balloon to ambient winds of a particularvelocity; determining that ambient winds of the particular velocity arelikely to be available at a particular altitude; and adjusting thealtitude of the target balloon to attain the particular altitude.
 3. Themethod of claim 1, wherein the target balloon and one or more neighborballoons are high-altitude balloons.
 4. The method of claim 1, whereinthe desired movement of the target balloon comprises a desired directionof movement.
 5. The method of claim 1, wherein the desired movement ofthe target balloon comprises a desired velocity.
 6. The method of claim1, wherein the desired movement of the target balloon comprises adesired distance of travel in a desired direction.
 7. The method ofclaim 1, wherein the communication system comprises a free-space opticalcommunication system.
 8. The method of claim 1, wherein thecommunication system comprises a radio frequency (RF) communicationsystem.
 9. The method of claim 1, wherein the target balloon and one ormore neighbor balloons are part of a mesh network of balloons.
 10. Themethod of claim 9, further comprising identifying a predetermined numberof nearest balloons in the mesh network as the one or more neighborballoons.
 11. The method of claim 9, further comprising identifying anyballoons in the mesh network that are within a predefined distance fromthe target balloon as the one or more neighbor balloons.
 12. The methodof claim 9, further comprising identifying any balloons in the meshnetwork that are within a communication range of the target balloon'scommunication system as the one or more neighbor balloons.
 13. Themethod of claim 1, wherein determining a desired movement of the targetballoon based on the determined locations of one or more neighborballoons relative to the determined location of the target ballooncomprises: defining a potential energy function that assigns a potentialenergy to the target balloon as a function of the determined locationsof the one or more neighbor balloons and the determined location of thetarget balloon; determining a gradient of the potential energy function;and determining the desired movement of the target balloon based on thegradient of the potential energy function.
 14. The method of claim 13,wherein determining the desired movement of the target balloon based onthe gradient comprises: determining a direction of the gradient; anddetermining a direction of the desired movement of the target balloonbased on the direction of the gradient.
 15. The method of claim 13,wherein determining the desired movement of the target balloon based onthe gradient comprises: determining a magnitude of the gradient; anddetermining a magnitude of the desired movement of the target balloonbased on the magnitude of the gradient.
 16. The method of claim 1,wherein the target balloon comprises an airfoil.
 17. The method of claim16, wherein the airfoil comprises a kite, wing, or sail.
 18. The methodof claim 16, wherein controlling the target balloon based on the desiredmovement of the target balloon comprises controlling the airfoil. 19.The method of claim 16, wherein the airfoil is operable to move thetarget balloon horizontally using ambient winds.
 20. The method of claim16, wherein the airfoil is operable to convert vertical motion of thetarget balloon into horizontal motion of the target balloon, and whereincontrolling the target balloon based on the desired movement of thetarget balloon comprises controlling a buoyancy of the target balloon.21. A balloon, comprising: a communication system operable for datacommunication with one or more other balloons in a mesh network ofballoons; and a controller coupled to the communication system, whereinthe controller is configured to: (a) determine the balloon's location;(b) determine locations of one or more neighbor balloons relative to theballoon's determined location, wherein the one or more neighbor balloonsare in the mesh network of balloons; (c) determine a desired movement ofthe balloon based on the determined locations of the one or moreneighbor balloons relative to the balloon's determined location, whereinthe desired movement of the balloon comprises a desired horizontalmovement of the balloon; and (d) control an altitude of the balloonbased on the desired horizontal movement.
 22. The balloon of claim 21,further comprising: an altitude-control system that is operable toadjust the altitude of the balloon, wherein the controller is configuredto control the altitude-control system based on the desired horizontalmovement of the balloon.
 23. The balloon of claim 21, wherein thecontroller is configured to determine the balloon's location using asatellite-based positioning system.
 24. The balloon of claim 21, whereinthe controller is configured to determine the locations of the one ormore neighbor balloons based on information received through thecommunication system.